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      SUBROUTINE <a name="STGEXC.1"></a><a href="stgexc.f.html#STGEXC.1">STGEXC</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                   LDZ, IFST, ILST, WORK, LWORK, INFO )
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  -- LAPACK routine (version 3.1) --
</span><span class="comment">*</span><span class="comment">     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd..
</span><span class="comment">*</span><span class="comment">     November 2006
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Scalar Arguments ..
</span>      LOGICAL            WANTQ, WANTZ
      INTEGER            IFST, ILST, INFO, LDA, LDB, LDQ, LDZ, LWORK, N
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Array Arguments ..
</span>      REAL               A( LDA, * ), B( LDB, * ), Q( LDQ, * ),
     $                   WORK( * ), Z( LDZ, * )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Purpose
</span><span class="comment">*</span><span class="comment">  =======
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  <a name="STGEXC.20"></a><a href="stgexc.f.html#STGEXC.1">STGEXC</a> reorders the generalized real Schur decomposition of a real
</span><span class="comment">*</span><span class="comment">  matrix pair (A,B) using an orthogonal equivalence transformation
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                 (A, B) = Q * (A, B) * Z',
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  so that the diagonal block of (A, B) with row index IFST is moved
</span><span class="comment">*</span><span class="comment">  to row ILST.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  (A, B) must be in generalized real Schur canonical form (as returned
</span><span class="comment">*</span><span class="comment">  by <a name="SGGES.29"></a><a href="sgges.f.html#SGGES.1">SGGES</a>), i.e. A is block upper triangular with 1-by-1 and 2-by-2
</span><span class="comment">*</span><span class="comment">  diagonal blocks. B is upper triangular.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Optionally, the matrices Q and Z of generalized Schur vectors are
</span><span class="comment">*</span><span class="comment">  updated.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">         Q(in) * A(in) * Z(in)' = Q(out) * A(out) * Z(out)'
</span><span class="comment">*</span><span class="comment">         Q(in) * B(in) * Z(in)' = Q(out) * B(out) * Z(out)'
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Arguments
</span><span class="comment">*</span><span class="comment">  =========
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  WANTQ   (input) LOGICAL
</span><span class="comment">*</span><span class="comment">          .TRUE. : update the left transformation matrix Q;
</span><span class="comment">*</span><span class="comment">          .FALSE.: do not update Q.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  WANTZ   (input) LOGICAL
</span><span class="comment">*</span><span class="comment">          .TRUE. : update the right transformation matrix Z;
</span><span class="comment">*</span><span class="comment">          .FALSE.: do not update Z.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  N       (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The order of the matrices A and B. N &gt;= 0.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  A       (input/output) REAL array, dimension (LDA,N)
</span><span class="comment">*</span><span class="comment">          On entry, the matrix A in generalized real Schur canonical
</span><span class="comment">*</span><span class="comment">          form.
</span><span class="comment">*</span><span class="comment">          On exit, the updated matrix A, again in generalized
</span><span class="comment">*</span><span class="comment">          real Schur canonical form.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDA     (input)  INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array A. LDA &gt;= max(1,N).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  B       (input/output) REAL array, dimension (LDB,N)
</span><span class="comment">*</span><span class="comment">          On entry, the matrix B in generalized real Schur canonical
</span><span class="comment">*</span><span class="comment">          form (A,B).
</span><span class="comment">*</span><span class="comment">          On exit, the updated matrix B, again in generalized
</span><span class="comment">*</span><span class="comment">          real Schur canonical form (A,B).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDB     (input)  INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array B. LDB &gt;= max(1,N).
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Q       (input/output) REAL array, dimension (LDZ,N)
</span><span class="comment">*</span><span class="comment">          On entry, if WANTQ = .TRUE., the orthogonal matrix Q.
</span><span class="comment">*</span><span class="comment">          On exit, the updated matrix Q.
</span><span class="comment">*</span><span class="comment">          If WANTQ = .FALSE., Q is not referenced.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDQ     (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array Q. LDQ &gt;= 1.
</span><span class="comment">*</span><span class="comment">          If WANTQ = .TRUE., LDQ &gt;= N.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Z       (input/output) REAL array, dimension (LDZ,N)
</span><span class="comment">*</span><span class="comment">          On entry, if WANTZ = .TRUE., the orthogonal matrix Z.
</span><span class="comment">*</span><span class="comment">          On exit, the updated matrix Z.
</span><span class="comment">*</span><span class="comment">          If WANTZ = .FALSE., Z is not referenced.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LDZ     (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The leading dimension of the array Z. LDZ &gt;= 1.
</span><span class="comment">*</span><span class="comment">          If WANTZ = .TRUE., LDZ &gt;= N.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  IFST    (input/output) INTEGER
</span><span class="comment">*</span><span class="comment">  ILST    (input/output) INTEGER
</span><span class="comment">*</span><span class="comment">          Specify the reordering of the diagonal blocks of (A, B).
</span><span class="comment">*</span><span class="comment">          The block with row index IFST is moved to row ILST, by a
</span><span class="comment">*</span><span class="comment">          sequence of swapping between adjacent blocks.
</span><span class="comment">*</span><span class="comment">          On exit, if IFST pointed on entry to the second row of
</span><span class="comment">*</span><span class="comment">          a 2-by-2 block, it is changed to point to the first row;
</span><span class="comment">*</span><span class="comment">          ILST always points to the first row of the block in its
</span><span class="comment">*</span><span class="comment">          final position (which may differ from its input value by
</span><span class="comment">*</span><span class="comment">          +1 or -1). 1 &lt;= IFST, ILST &lt;= N.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  WORK    (workspace/output) REAL array, dimension (MAX(1,LWORK))
</span><span class="comment">*</span><span class="comment">          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  LWORK   (input) INTEGER
</span><span class="comment">*</span><span class="comment">          The dimension of the array WORK.
</span><span class="comment">*</span><span class="comment">          LWORK &gt;= 1 when N &lt;= 1, otherwise LWORK &gt;= 4*N + 16.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">          If LWORK = -1, then a workspace query is assumed; the routine
</span><span class="comment">*</span><span class="comment">          only calculates the optimal size of the WORK array, returns
</span><span class="comment">*</span><span class="comment">          this value as the first entry of the WORK array, and no error
</span><span class="comment">*</span><span class="comment">          message related to LWORK is issued by <a name="XERBLA.110"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  INFO    (output) INTEGER
</span><span class="comment">*</span><span class="comment">           =0:  successful exit.
</span><span class="comment">*</span><span class="comment">           &lt;0:  if INFO = -i, the i-th argument had an illegal value.
</span><span class="comment">*</span><span class="comment">           =1:  The transformed matrix pair (A, B) would be too far
</span><span class="comment">*</span><span class="comment">                from generalized Schur form; the problem is ill-
</span><span class="comment">*</span><span class="comment">                conditioned. (A, B) may have been partially reordered,
</span><span class="comment">*</span><span class="comment">                and ILST points to the first row of the current
</span><span class="comment">*</span><span class="comment">                position of the block being moved.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Further Details
</span><span class="comment">*</span><span class="comment">  ===============
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  Based on contributions by
</span><span class="comment">*</span><span class="comment">     Bo Kagstrom and Peter Poromaa, Department of Computing Science,
</span><span class="comment">*</span><span class="comment">     Umea University, S-901 87 Umea, Sweden.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  [1] B. Kagstrom; A Direct Method for Reordering Eigenvalues in the
</span><span class="comment">*</span><span class="comment">      Generalized Real Schur Form of a Regular Matrix Pair (A, B), in
</span><span class="comment">*</span><span class="comment">      M.S. Moonen et al (eds), Linear Algebra for Large Scale and
</span><span class="comment">*</span><span class="comment">      Real-Time Applications, Kluwer Academic Publ. 1993, pp 195-218.
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">  =====================================================================
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     .. Parameters ..
</span>      REAL               ZERO
      PARAMETER          ( ZERO = 0.0E+0 )
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Local Scalars ..
</span>      LOGICAL            LQUERY
      INTEGER            HERE, LWMIN, NBF, NBL, NBNEXT
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. External Subroutines ..
</span>      EXTERNAL           <a name="STGEX2.144"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>, <a name="XERBLA.144"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Intrinsic Functions ..
</span>      INTRINSIC          MAX
<span class="comment">*</span><span class="comment">     ..
</span><span class="comment">*</span><span class="comment">     .. Executable Statements ..
</span><span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Decode and test input arguments.
</span><span class="comment">*</span><span class="comment">
</span>      INFO = 0
      LQUERY = ( LWORK.EQ.-1 )
      IF( N.LT.0 ) THEN
         INFO = -3
      ELSE IF( LDA.LT.MAX( 1, N ) ) THEN
         INFO = -5
      ELSE IF( LDB.LT.MAX( 1, N ) ) THEN
         INFO = -7
      ELSE IF( LDQ.LT.1 .OR. WANTQ .AND. ( LDQ.LT.MAX( 1, N ) ) ) THEN
         INFO = -9
      ELSE IF( LDZ.LT.1 .OR. WANTZ .AND. ( LDZ.LT.MAX( 1, N ) ) ) THEN
         INFO = -11
      ELSE IF( IFST.LT.1 .OR. IFST.GT.N ) THEN
         INFO = -12
      ELSE IF( ILST.LT.1 .OR. ILST.GT.N ) THEN
         INFO = -13
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.EQ.0 ) THEN
         IF( N.LE.1 ) THEN
            LWMIN = 1
         ELSE
            LWMIN = 4*N + 16
         END IF
         WORK(1) = LWMIN
<span class="comment">*</span><span class="comment">
</span>         IF (LWORK.LT.LWMIN .AND. .NOT.LQUERY) THEN
            INFO = -15
         END IF
      END IF
<span class="comment">*</span><span class="comment">
</span>      IF( INFO.NE.0 ) THEN
         CALL <a name="XERBLA.185"></a><a href="xerbla.f.html#XERBLA.1">XERBLA</a>( <span class="string">'<a name="STGEXC.185"></a><a href="stgexc.f.html#STGEXC.1">STGEXC</a>'</span>, -INFO )
         RETURN
      ELSE IF( LQUERY ) THEN
         RETURN
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Quick return if possible
</span><span class="comment">*</span><span class="comment">
</span>      IF( N.LE.1 )
     $   RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Determine the first row of the specified block and find out
</span><span class="comment">*</span><span class="comment">     if it is 1-by-1 or 2-by-2.
</span><span class="comment">*</span><span class="comment">
</span>      IF( IFST.GT.1 ) THEN
         IF( A( IFST, IFST-1 ).NE.ZERO )
     $      IFST = IFST - 1
      END IF
      NBF = 1
      IF( IFST.LT.N ) THEN
         IF( A( IFST+1, IFST ).NE.ZERO )
     $      NBF = 2
      END IF
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     Determine the first row of the final block
</span><span class="comment">*</span><span class="comment">     and find out if it is 1-by-1 or 2-by-2.
</span><span class="comment">*</span><span class="comment">
</span>      IF( ILST.GT.1 ) THEN
         IF( A( ILST, ILST-1 ).NE.ZERO )
     $      ILST = ILST - 1
      END IF
      NBL = 1
      IF( ILST.LT.N ) THEN
         IF( A( ILST+1, ILST ).NE.ZERO )
     $      NBL = 2
      END IF
      IF( IFST.EQ.ILST )
     $   RETURN
<span class="comment">*</span><span class="comment">
</span>      IF( IFST.LT.ILST ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Update ILST.
</span><span class="comment">*</span><span class="comment">
</span>         IF( NBF.EQ.2 .AND. NBL.EQ.1 )
     $      ILST = ILST - 1
         IF( NBF.EQ.1 .AND. NBL.EQ.2 )
     $      ILST = ILST + 1
<span class="comment">*</span><span class="comment">
</span>         HERE = IFST
<span class="comment">*</span><span class="comment">
</span>   10    CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Swap with next one below.
</span><span class="comment">*</span><span class="comment">
</span>         IF( NBF.EQ.1 .OR. NBF.EQ.2 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Current block either 1-by-1 or 2-by-2.
</span><span class="comment">*</span><span class="comment">
</span>            NBNEXT = 1
            IF( HERE+NBF+1.LE.N ) THEN
               IF( A( HERE+NBF+1, HERE+NBF ).NE.ZERO )
     $            NBNEXT = 2
            END IF
            CALL <a name="STGEX2.248"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                   LDZ, HERE, NBF, NBNEXT, WORK, LWORK, INFO )
            IF( INFO.NE.0 ) THEN
               ILST = HERE
               RETURN
            END IF
            HERE = HERE + NBNEXT
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Test if 2-by-2 block breaks into two 1-by-1 blocks.
</span><span class="comment">*</span><span class="comment">
</span>            IF( NBF.EQ.2 ) THEN
               IF( A( HERE+1, HERE ).EQ.ZERO )
     $            NBF = 3
            END IF
<span class="comment">*</span><span class="comment">
</span>         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Current block consists of two 1-by-1 blocks, each of which
</span><span class="comment">*</span><span class="comment">           must be swapped individually.
</span><span class="comment">*</span><span class="comment">
</span>            NBNEXT = 1
            IF( HERE+3.LE.N ) THEN
               IF( A( HERE+3, HERE+2 ).NE.ZERO )
     $            NBNEXT = 2
            END IF
            CALL <a name="STGEX2.273"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                   LDZ, HERE+1, 1, NBNEXT, WORK, LWORK, INFO )
            IF( INFO.NE.0 ) THEN
               ILST = HERE
               RETURN
            END IF
            IF( NBNEXT.EQ.1 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Swap two 1-by-1 blocks.
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="STGEX2.283"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                      LDZ, HERE, 1, 1, WORK, LWORK, INFO )
               IF( INFO.NE.0 ) THEN
                  ILST = HERE
                  RETURN
               END IF
               HERE = HERE + 1
<span class="comment">*</span><span class="comment">
</span>            ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Recompute NBNEXT in case of 2-by-2 split.
</span><span class="comment">*</span><span class="comment">
</span>               IF( A( HERE+2, HERE+1 ).EQ.ZERO )
     $            NBNEXT = 1
               IF( NBNEXT.EQ.2 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                 2-by-2 block did not split.
</span><span class="comment">*</span><span class="comment">
</span>                  CALL <a name="STGEX2.301"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
     $                         Z, LDZ, HERE, 1, NBNEXT, WORK, LWORK,
     $                         INFO )
                  IF( INFO.NE.0 ) THEN
                     ILST = HERE
                     RETURN
                  END IF
                  HERE = HERE + 2
               ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                 2-by-2 block did split.
</span><span class="comment">*</span><span class="comment">
</span>                  CALL <a name="STGEX2.313"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
     $                         Z, LDZ, HERE, 1, 1, WORK, LWORK, INFO )
                  IF( INFO.NE.0 ) THEN
                     ILST = HERE
                     RETURN
                  END IF
                  HERE = HERE + 1
                  CALL <a name="STGEX2.320"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
     $                         Z, LDZ, HERE, 1, 1, WORK, LWORK, INFO )
                  IF( INFO.NE.0 ) THEN
                     ILST = HERE
                     RETURN
                  END IF
                  HERE = HERE + 1
               END IF
<span class="comment">*</span><span class="comment">
</span>            END IF
         END IF
         IF( HERE.LT.ILST )
     $      GO TO 10
      ELSE
         HERE = IFST
<span class="comment">*</span><span class="comment">
</span>   20    CONTINUE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">        Swap with next one below.
</span><span class="comment">*</span><span class="comment">
</span>         IF( NBF.EQ.1 .OR. NBF.EQ.2 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Current block either 1-by-1 or 2-by-2.
</span><span class="comment">*</span><span class="comment">
</span>            NBNEXT = 1
            IF( HERE.GE.3 ) THEN
               IF( A( HERE-1, HERE-2 ).NE.ZERO )
     $            NBNEXT = 2
            END IF
            CALL <a name="STGEX2.349"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                   LDZ, HERE-NBNEXT, NBNEXT, NBF, WORK, LWORK,
     $                   INFO )
            IF( INFO.NE.0 ) THEN
               ILST = HERE
               RETURN
            END IF
            HERE = HERE - NBNEXT
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Test if 2-by-2 block breaks into two 1-by-1 blocks.
</span><span class="comment">*</span><span class="comment">
</span>            IF( NBF.EQ.2 ) THEN
               IF( A( HERE+1, HERE ).EQ.ZERO )
     $            NBF = 3
            END IF
<span class="comment">*</span><span class="comment">
</span>         ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">           Current block consists of two 1-by-1 blocks, each of which
</span><span class="comment">*</span><span class="comment">           must be swapped individually.
</span><span class="comment">*</span><span class="comment">
</span>            NBNEXT = 1
            IF( HERE.GE.3 ) THEN
               IF( A( HERE-1, HERE-2 ).NE.ZERO )
     $            NBNEXT = 2
            END IF
            CALL <a name="STGEX2.375"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                   LDZ, HERE-NBNEXT, NBNEXT, 1, WORK, LWORK,
     $                   INFO )
            IF( INFO.NE.0 ) THEN
               ILST = HERE
               RETURN
            END IF
            IF( NBNEXT.EQ.1 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">              Swap two 1-by-1 blocks.
</span><span class="comment">*</span><span class="comment">
</span>               CALL <a name="STGEX2.386"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ, Z,
     $                      LDZ, HERE, NBNEXT, 1, WORK, LWORK, INFO )
               IF( INFO.NE.0 ) THEN
                  ILST = HERE
                  RETURN
               END IF
               HERE = HERE - 1
            ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">             Recompute NBNEXT in case of 2-by-2 split.
</span><span class="comment">*</span><span class="comment">
</span>               IF( A( HERE, HERE-1 ).EQ.ZERO )
     $            NBNEXT = 1
               IF( NBNEXT.EQ.2 ) THEN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                 2-by-2 block did not split.
</span><span class="comment">*</span><span class="comment">
</span>                  CALL <a name="STGEX2.403"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
     $                         Z, LDZ, HERE-1, 2, 1, WORK, LWORK, INFO )
                  IF( INFO.NE.0 ) THEN
                     ILST = HERE
                     RETURN
                  END IF
                  HERE = HERE - 2
               ELSE
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">                 2-by-2 block did split.
</span><span class="comment">*</span><span class="comment">
</span>                  CALL <a name="STGEX2.414"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
     $                         Z, LDZ, HERE, 1, 1, WORK, LWORK, INFO )
                  IF( INFO.NE.0 ) THEN
                     ILST = HERE
                     RETURN
                  END IF
                  HERE = HERE - 1
                  CALL <a name="STGEX2.421"></a><a href="stgex2.f.html#STGEX2.1">STGEX2</a>( WANTQ, WANTZ, N, A, LDA, B, LDB, Q, LDQ,
     $                         Z, LDZ, HERE, 1, 1, WORK, LWORK, INFO )
                  IF( INFO.NE.0 ) THEN
                     ILST = HERE
                     RETURN
                  END IF
                  HERE = HERE - 1
               END IF
            END IF
         END IF
         IF( HERE.GT.ILST )
     $      GO TO 20
      END IF
      ILST = HERE
      WORK( 1 ) = LWMIN
      RETURN
<span class="comment">*</span><span class="comment">
</span><span class="comment">*</span><span class="comment">     End of <a name="STGEXC.438"></a><a href="stgexc.f.html#STGEXC.1">STGEXC</a>
</span><span class="comment">*</span><span class="comment">
</span>      END

</pre>

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